读下面的地质剖面示意图，回答下列各题。

已知函数  $f\left(x\right)=\left\{\begin{array}{c}\left(2-a\right)x-\frac{a}{2},\left(x<1\right)\\ {\log }_{a}x,(x\ge 1)\end{array}\right.$是R上的增函数，那么实数a的取值范围是____．

根据材料内容，选择正确答案。

    Mr Smith had a week's holiday, so he said, "I'm going to see the sea by train." He put on his best clothes, took a small bag, went to the railway station and got onto the train. He wore a beautiful hat, and he often put his head out of the window during the trip and looked at the beautiful scenery. But suddenly the wind pulled his hat off.

    Mr Smith took his old bag and threw it out of the window quickly too. The others in the train laughed. "Is your bag going to bring back your beautiful hat?" they asked.

    "N0," Mr Smith answered, "but there is no name or address in my hat, and there's a name and an address on the bag. If someone finds both of them, he or she will send me the bag and the hat.''